The invention relates to an x-ray collimator (primary radiation diaphragm) comprising at least two pairs of collimator plates, staggered 90.degree., wherein the plates of each plate pair are commonly adjustable symmetrically to the longitudinal axis of the collimator, and comprising a light-beam localizer (or light visor) for rendering visible the collimated field, exhibiting a light source which emits a beam of light bounded by the collimator plates.
An x-ray apparatus equipped with a light beam localizer arrangement for marking the extent of the x-ray beam is known from the U.S. Pat. No. 2,955,205. The light source radiates onto an x-ray-transmissive mirror disposed in the path of the x-rays and inclined in relation to the central ray of the x-radiation. The disadvantage of this light beam localizer consists in that the light rays of the light source are directed not only onto the mirror, but that they issue from the light source in all directions. Therefore, a light source with a high power must be employed which is expensive and susceptible to failure, and which entails cooling problems.